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Discussion Starter #1
My 5m was running poorly as of the tail end of my last rip in my '85. I pulled the plugs and found that the gap on #4 had closed right down to just about nothing. This was the problem as she is running superbly again now. What might cause this? I currently have some cheap ass Delco plugs in it as my new NGK's are on the way.

While I had the plugs out I decided to do a compression test. I came up with:

1- 146
2- 150
3- 143
4- 134
5- 134
6- 142

I know this is low in all cylinders. I have a slightly shaved and ported head as well, so I expected the comp's to be higher. I had not checked the compression for about 18 months. I was in the 160's in some cylinders then (before I rebuilt the head). I do burn a good deal of oil so it would only stand to reason that I could use new rings (I did not drop some oil in the chamber and re-test compression, maybe I should have) I have been looking for a good reason to buy a 6m and rebuild it, but this 5M seems to run really strong especially after my recent acquisition of a DT header and Brullen exhaust system. Am I missing a lot of HP with these compression numbers? Sorry for the ridiculously long post. :p
 

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yeah probably. I"m in the same boat. About 155 to 145 in all of mine, it should be 180. I rebuilt the head in my 82 and what huge difference that made, perfect 180 in every cylinder after that.
 

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How many compression strokes did it take for the compression gauge to read in the 130's, 140's?? Your compression gauge should shoot right up to max. compression pressure with just one or two compression strokes if the rings are in good shape.
 

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Discussion Starter #4
I turned it over 3-4 times for each reading, I did not have an assistant to crank it over while I watched the guage, so I don't know if it shot right up or not. I think the rings are pretty bad as I am burning a lot of oil and the head is fresh. I should have done the bottom end when I had the head off. Maybe I will get a 6M longblock and rebuild it outside of the car. Or maybe I will pull the 5M and rebuild it over the winter.
 
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